Rights group Human Rights Watch (HRW) called on Greece to immediately end the holding of unaccompanied migrant children in police station cells, saying the country must find space for them in facilities where they can receive adequate care. HRW in an announcement said a shortage of places in shelters had led to "arbitrary prolonged detention in places unfit for children." The group said that according to Greece's state-run National Center for Social Solidarity, about 18 children were awaiting transfer at police stations, and hundreds were in overcrowded detention camps.

Children as young as 14 were found in police cells according to HRW's Eva Cosse. "It's a gross indictment of the government's failure to care for these children. They shouldn't spend even one more day in these awful cells," she told the Associated Press on Wednesday.

"In the long term, the government should increase capacity in dedicated shelters for unaccompanied migrant children. But even before that, authorities should put an immediate end to the detention of children in police station cells."

Greece has been the main entry point for hundreds of thousands of refugees and migrants heading to Europe.

Nearly 50,000 asylum seekers are on the Greek mainland at government-run camps awaiting to be formally granted residence rights in Greece or to be relocated to other EU countries.

Thirty-one percent of the million migrants and refugees who arrived in the EU last year were children, while minors currently make up a quarter of daily asylum applications, according to data gathered by the European Commission.

In the announcement published on Tuesday, HRW said it had interviewed 11 children who had been detained for as long as two months. "The children described unsanitary, overcrowded cells, including dirty blankets and bugs, and lack of access to information or services such as counseling and legal aid," the announcement said. Government officials did not immediately respond to requests for comment.